Pentagonite is a rare secondary mineral typically found as stunning deep-blue radiating sprays or bow-tie clusters within volcanic vugs. It is chemically dimorphous with its much more common sister mineral, Cavansite, but displays a distinct orthorhombic crystal structure. Collectors prize it for its intense, vibrant color and aesthetic crystal habits, found almost exclusively in the Deccan Traps basalt quarries of India.
Is this pentagonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch pentagonite with a known reference. Pentagonite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pentagonite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Pentagonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: deep blue, azure blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: spray of radiating acicular crystals, bow-tie aggregates.
Often confused with
Pentagonite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside pentagonite
Minerals reported to co-occur with pentagonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(V⁴⁺O)Si₄O₁₀·4H₂O
- Mohs hardness
- 3-4
- Density
- 2.33 g/cm³
- Colors
- Streak
- Pale Blue
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Spray of Radiating Acicular Crystals, Bow-tie Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Basaltic Vugs in Volcanic Rock
- Typical price
- $20-200 thumbnail, $300-1500+ specimen
Where rockhounds find pentagonite
Classic worldwide localities
- Wagholi Quarry, Pune, India
- Deccan Traps, India
Field-hunting tip
Look in basaltic vugs in volcanic rock country — that is the host setting where pentagonite typically forms. If you start seeing cavansite, heulandite, stilbite in float, you are in the right ground. Field specimens usually show a spray of radiating acicular crystals, bow-tie aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pentagonite?+
Where is pentagonite found?+
How much is pentagonite worth?+
What rocks look like pentagonite?+
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Find pentagonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
